Electric machine with stator windings having over-under end loops

ABSTRACT

A multi-phase electric machine having plurality of windings are mounted on the stator core and define a plurality of phases with each phase having at least two parallel windings. A standard pitch is defined between each pole of each phase, the pitch being a common circumferential spacing between corresponding slots of each pole. Each of the windings has a position change end loop at the same location, wherein the position change end loops define a non-standard pitch to thereby change the relative positions of the parallel windings in the slots. At each set of such position change end loops, the windings defining a greater pitch extend over the windings defining a lesser pitch.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119(e) of U.S.provisional patent application Ser. No. 62/368,070 filed on Jul. 28,2016 entitled ELECTRIC MACHINE WITH STATOR HAVING PHASE SHIFT WINDINGS;U.S. provisional patent application Ser. No. 62/368,104 filed on Jul.28, 2016 entitled ELECTRIC MACHINE WITH STATOR HAVING EVEN SLOTDISTRIBUTION; and U.S. provisional patent application Ser. No.62/373,223 filed on Aug. 10, 2016 entitled ELECTRIC MACHINE WITH STATORWINDINGS HAVING OVER-UNDER END LOOPS; the disclosures of each of whichare hereby incorporated herein by reference.

BACKGROUND

The present invention relates to electric machines.

Electric machines are used for several different purposes in modernvehicles. For example, electric machines are commonly employed asstarters, alternators, traction motors and for other purposes. In theseapplications, the electric machine may act as a motor, generator or beselectively operable as either a motor or a generator.

There is an increasing demand for electric machines used in vehicleapplications, as well as other non-vehicular applications, for anelectric machine with reduced size and increased efficiency.

Improvements in electric machine design which allow for cost efficientmanufacture while meeting the increasingly stringent demands of modernvehicular applications are desirable.

SUMMARY

The present invention provides an electric machine having a windingpattern with end loops that alter the relative position of theindividual windings of a phase having a plurality of parallel windingsand which allows for the cost efficient manufacture of a compact andefficient electric machine.

The invention comprises, in one form thereof, a multi-phase electricmachine that includes a stator operably coupled with a rotor wherein therotor is rotatable relative to the stator. The stator includes a statorcore defining a central opening and a plurality of axially extendingslots which circumscribe the central opening. A plurality of windingsare mounted on the stator core wherein the plurality of windings definea plurality of phases and wherein, for each phase, the plurality ofwindings include at least two parallel windings. The stator assemblydefines a standard pitch between each pole of each phase, the pitchbeing a common circumferential spacing between corresponding slots ofeach pole. Each of the parallel windings includes at least one positionchange end loop, wherein each of the parallel windings has one of theposition change end loops at the same location, wherein the positionchange end loops define a non-standard pitch to thereby change therelative positions of the parallel windings in the slots.

In some embodiments, each phase includes at least three windingsconnected in parallel. In such an embodiment having at least threewindings, the position change end loops may be arranged such that afirst set of position change end loops is disposed between a selectedpole and an adjacent pole and wherein a first winding of the first setof position change end loops is disposed at one of the clockwise andcounterclockwise ends of the pole at the selected pole and is disposedat the other of the clockwise and counterclockwise ends of the pole atthe adjacent pole, the remaining windings of the first set of positionchange end loops each being shifted one by one slot.

In some embodiments the windings may be arranged such that the firstwinding defines a pitch that is greater than the standard pitch betweenthe first and second poles and the remaining windings each define apitch that is one less than the standard pitch between the selected andadjacent poles. In such an embodiment, the first winding may extend overthe remaining windings between the selected and adjacent poles. Whensuch an embodiment has exactly three windings per phase, the firstwinding may define a pitch that is two slots greater than the standardpitch between the selected and adjacent poles.

In some embodiments having three windings wherein the first windingmoves from one end of the selected pole to the opposite end of theadjacent pole, the first winding defines a pitch that is less than thestandard pitch between the selected and adjacent poles and the remainingwindings each define a pitch that is one greater than the standard pitchbetween the selected and adjacent poles. In such an embodiment, theremaining windings may extend over the top of the first winding betweenthe selected and adjacent poles. When such an embodiment includesexactly three windings per phase, the first winding may define a pitchthat is two slots less than the standard pitch between the selected andadjacent poles.

In some embodiments of the electric machine, at each set of positionchange end loops, the windings defining a greater pitch extend over thewindings defining a lesser pitch. In such an embodiment, the windingsmay define a phase shift wherein for each pole, there are a greaternumber of slots than windings. Such an embodiment may also includewindings wherein each winding includes a plurality of position changeend loops.

In the various embodiments described above, the electric machine may bea three phase electric machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features of this invention, and the mannerof attaining them, will become more apparent and the invention itselfwill be better understood by reference to the following description ofan embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a partial winding diagram showing three wires defining a partof an individual phase.

FIG. 2 is a partial winding diagram showing three wires that areconnected in series with the wires depicted in FIG. 1 to form anindividual phase.

FIG. 3 is a top view of a stator diagram illustrating the arrangement ofthe wires of FIGS. 1 and 2.

FIG. 4 is a detail view of a portion of the stator diagram of FIG. 3.

FIG. 5 is another detail view of a portion of the stator diagram of FIG.3.

FIG. 6 is a cross sectional view of an electric machine.

FIG. 7A is a side view showing three standard pitch end loops.

FIG. 7B is a top view showing three standard pitch end loops.

FIG. 7C is a perspective view showing three standard pitch end loops.

FIG. 8A is a side view showing position change end loops with two endloops extending over a third end loop.

FIG. 8B is a top view showing the end loops of FIG. 8A.

FIG. 8C is a perspective view showing the end loops of FIG. 8A.

FIG. 9A is a side view showing position change end loops with one endloop extending over two other end loops.

FIG. 9B is a top view showing the end loops of FIG. 9A.

FIG. 9C is a perspective view showing the end loops of FIG. 9A.

FIG. 10A is a top view showing one end loop extending over two other endloops.

FIG. 10B is a perspective view showing the end loops of FIG. 10A.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the exemplification set outherein illustrates an embodiment of the invention, in one form, theembodiment disclosed below is not intended to be exhaustive or to beconstrued as limiting the scope of the invention to the precise formdisclosed.

DETAILED DESCRIPTION

FIG. 6 illustrates an electric machine 20. In the illustratedembodiment, electric machine 20 is an automotive alternator capable ofoperating as a motor or as a generator, however, alternative embodimentsmay take the form of an electric machine that is solely operable as amotor or solely operable as a generator. Electric machine 20 includes arotor 22 mounted on a shaft 24 which both rotate relative to stator 26.Stator 26 has a stator core 28 and a plurality of windings 30.

Stator core 28 may be formed out of a stack of laminations and defines aplurality of slots 32. Windings 30 include axially extending segments 34that are disposed within slots 32 and end turns 36 with each end turn 36connecting a pair of slot segments 34. Axially extending slots 32circumscribe central opening 38 of stator core 28.

The illustrated embodiment is a three phase electric machine with sixturns. Additionally, each phase includes three windings arranged inparallel. In other words, each winding extends about the fullcircumference of the stator core six times and there are three suchwindings for each phase. To achieve this arrangement two separate wiresor filars are used for each winding whereby a total of six separatewires or filars are used for each phase. Each of the individual wiresform three turns about the stator and is connected in series withanother one of the wires to thereby form one of the three windings ofeach phase.

One parameter that may be used to describe a winding arrangement isslots per pole per phase. This is equal to the number of slots per polein each slot group of the winding if each such slot were filled solelyby windings of one phase. For example, in the illustrated embodiment,there are 18 slot segments in each slot group and each slot holds 6 slotsegments therefore the illustrated arrangement has 3 slots per pole perphase. The illustrated embodiment, however, has what is known as a phaseshift and some slots hold slot segments of two different phases.

The use such phase shifting can reduce what is known as the skin effect.As a general rule, when the conductors in a particular slot carrydifferent phase currents, the skin effect in such conductors will beless than if all of the conductors in the slot carried the same phasecurrent. While such phase shifting reduces the skin effect, the use ofsuch phase shifting can make it more difficult to electrically balancethe windings.

To avoid or minimize a re-circulating current in the winding, it isdesirable for the winding to be electrically balanced this isparticularly true for a winding having a plurality of wires connected inparallel. Providing an electrically balanced stator can be particularlydifficult if phase shifting is employed and each phase is formed by anodd number of windings arranged in parallel.

The illustrated embodiment provides a stator winding pattern whichprovides an electrically balanced stator with phase shifting and an oddnumber of windings arranged in parallel for each phase. As mentionedabove, the illustrated winding pattern includes six turns and threeseparate windings for each phase. The pattern has three slots per poleper phase but windings occupy four physical slots for each pole or slotgroup. In each slot group, the two center slots each have six conductorswhich are all from the same phase. The two outer slots each have threeconductors from one phase and three additional conductors from adifferent phase. To electrically balance the stator, each slot of theslot group needs to have an equal number of conductors from each of thethree windings. It is also desirable for each of the different radiallayers to have an equal number of conductors from each of the threewindings.

This radial balancing, however, is less important than the balancingbetween slots. The exemplary winding pattern can be used to provide anelectrically balanced stator and is further described below with the aidof FIGS. 1-5.

FIG. 1 illustrates three separate wires X, Y, Z that are connected inseries with the three separate wires A, B, C illustrated in FIG. 2. Morespecifically, wire A is connected in series with wire Z to form a firstwinding, wire B is connected in series with wire X to form a secondwinding and wire C is connected in series with wire Y to form a thirdwinding. The first, second and third windings are then connected inparallel to form one phase of electric machine 20. Electric machine 20is a three phase electric machine and two additional phases having thesame winding arrangement are also employed with electric machine 20.

As can be seen in FIG. 3, each phase of the stator assembly defines 16poles with each pole being formed by four physical slots. Six wires fitwithin each axially extending stator slot 32. As used herein, theradially outermost wire is in layer 1, layer 2 being the next radiallyinward wire position and so on with the radially innermost wire positionbeing layer 6.

As can also be seen in FIG. 3, as well as FIGS. 4 and 5, each of thepoles is formed by a group of four slots wherein the two central slotsare each completely filled with windings (six windings in theillustrated embodiment) and two outer slots that are only half filledwith windings from a particular phase (three windings in the illustratedembodiment) to thereby form a 3-6-6-3 winding pattern. As used herein,and as labelled in FIG. 4 for slot 15 and slot 3, starting at the outerslot on the counterclockwise side of each slot group forming a pole andmoving clockwise, the slots are referred to as slot AA, slot BB, slot CCand slot DD. In other words, slots BB and CC form the central slots andslots AA and DD form the outer slots.

The distance between slot AA of one pole and slot AA of the adjacentpoles is 9 slots. Similarly, the distance between slot BB of one poleand slot BB of the adjacent poles is 9 slots and so on, this distancebetween corresponding slots of the slot groups forming adjacent polesdefines the standard pitch of the electric machine. In the illustratedembodiment, the standard pitch is 9 slots.

Returning to FIGS. 1 and 2, the wiring diagrams label any pitch betweenslot segments that is non-standard. The location of the numberindicating the non-standard pitch also indicates at which axial end ofthe stator the end loop forming the non-standard pitch is located. It isalso noted that the wiring diagrams of FIGS. 1 and 2 also indicate inwhich layer position the wires are located.

As most easily seen in FIGS. 3-5, the windings in slot AA are positionedin the radial outermost layers, i.e., layers 1, 2 and 3 while thewindings in slot DD are positioned in the radial innermost layers, i.e.,layers 4, 5 and 6. When all of the phases have this same pattern, slotAA of one phase will correspond and overlap with slot DD of an adjacentphase allowing the outer slots to be completely filled with windings.FIGS. 3-5 illustrate the windings of only one phase except for the spacebetween poles 2 and 3 of FIG. 4. This portion of FIG. 4 illustrates thelocation of the windings from a second phase (indicated by filled-inwire outlines) and the location of the windings from a third phase(indicated by the hollow wire outlines). This clearly shows how theouter slots of each phase overlap such that each outer slot includeswindings from two different phases.

It is further noted that while the outer slots of the illustratedembodiment have windings wherein the windings from one phase are allpositioned in the radially outer most layers and the windings from theother phase are all positioned in the radially innermost layers, otherconfigurations are also possible. For example, the windings from thedifferent phases could alternate. In the illustrated embodiment thiscould be achieved by having windings in layers 1, 3 and 5 in slot AA andin layers 2, 4 and 6 in slot DD. Such an arrangement, however, would bemore difficult to manufacture than the illustrated embodiment and wouldrequire a more complex winding pattern.

To control the position of the windings in the outer slots, special endloops referred to herein as phase shift end loops are used. In theillustrated embodiment, each phase includes three windings that areconnected in parallel. With each winding being formed by two continuouswires that joined together at their ends to thereby form one long filarthat forms one of the parallel windings. The number of parallel windingsis one less than the number of physical slots used to form each pole.Thus, for each wrap or turn the windings make about the stator core, thethree windings can be used to fill each central slot, BB, CC and one ofthe outer slots, AA, BB as depicted in the illustrated embodiment. Byforming all three windings with a phase shift end loop at a particularspot between two poles wherein the phase shift end loops are all oneslot different than the standard pitch end loops, the wires can beshifted from the three most counterclockwise slots of each pole to thethree most clockwise slots of each pole or visa versa.

For example, in FIG. 1, at the point where wires X, Y and Z transitionfrom layer 3 to layer 4, all three end loops have a 10 pitch end loopthat function as phase shift end loops. In other words, after completingtwo wraps or turns, the wires X, Y, Z have a phase shift end loop. Thisis also seen in FIG. 4 wherein at pole 15 in layer 3, wire X is in slotAA, wire Y is in slot BB and wire Z is in slot CC as a result of the 10pitch phase shift end loops, wire X is in slot BB, wire Y is slot CC andwire Z is in slot DD at pole 16 in layer 4. In the illustrated example,these phase shift end loops occur at the point where the windingstransition from layer 3 to layer 4. This is necessary to maintain thepattern wherein the windings are in slot AA in layers 1, 2 and 3 and arein slot DD in layers 4, 5 and 6. If an alternating pattern were employedfor the two different phases in the outer slots, a larger number ofphase shift end loops would be required.

Wires A, B and C also have phase shift end loops as can be seen withreference to FIGS. 2 and 4. After completing one wrap or turn, wires A,B, C have a phase shift end loop. This can be seen in FIG. 2 where thewires A, B, C transition from layer 3 to layer 4. This is also seen inFIG. 4 wherein at pole 16 in layer 3, wire B is in slot AA, wire C is inslot BB and wire A is in slot CC as a result of the 10 pitch phase shiftend loops, wire B is in slot BB, wire C is slot CC and wire A is in slotDD at pole 1 in layer 4.

To provide an electrically balanced winding pattern, each of theparallel windings needs to be in each slot central slot, BB, CC, anequal number of times and needs to be in each outer slot, AA, DD, anequal number of times. For the illustrated embodiment, the fill ratiobetween the central slots, BB, CC and the outer slots AA, DD is 2:1 and,thus, each winding needs to be disposed in the central slots twice asmany times as it is disposed in the outer slots. Position change endloops which shuffle the relative position of the windings in pole slotsare used to achieve this balance.

In the illustrated example, each set of wires A, B, C and X, Y, Z aresubject to position change end loops to alter the relative position ofthe wires at three locations for a total of six such locations. Turningfirst to FIGS. 1, 4 and 5, it can be seen that wires X, Y and Z aresubject to three position changes. At the interval between poles 8 and 9when wires X, Y and Z are in layer 1, a set of position change end loopsare used to alter the relative positions of wires X, Y and Z. At thislocation, the end loop wire X has a pitch of 11 slots while the endloops for wires Y and Z each have a pitch of 8 slots. As a result, wireX moves from slot AA at pole 8 to slot CC at pole 9, wire Y moves fromslot BB at pole 8 to slot AA at pole 9 and wire Z moves from slot CC atpole 8 to slot BB at pole 9.

Wires X, Y, Z are subject to another position change at the intervalbetween pole 8 and 9 when the wires are in layer 3. See FIGS. 1 and 5.This position change involves wire X having a position change end loopwith a pitch of 7 slots, wire Y having a position change end loop with apitch of 10 slots and wire Z having a position change end loop with apitch of 10 slots. As a result, in layer 3, wire X moves from slot CC atpole 8 to slot AA at pole 9, wire Y moves from slot AA at pole 8 to slotBB at pole 9 and wire Z moves from slot BB at pole 8 to slot CC at pole9.

Wires X, Y, Z are subject to a third position change at the intervalbetween poles 16 and 1 as the wires shift from layer 4 to layer 5. SeeFIGS. 1 and 4. This position change involves wire X having a positionchange end loop with a pitch of 11 slots, wire Y having a positionchange end loop with a pitch of 8 slots and wire Z having a positionchange end loop with a pitch of 8 slots. Each of these position changeend loops also move wires X, Y, Z from layer 4 at pole 16 to layer 5 atpole 1. Thus, wire X moves from slot BB at pole 16 to slot DD at pole 1,wire Y moves from slot CC at pole 16 to slot BB at pole 1 and wire Zmoves from slot DD at pole 16 to slot CC at pole 1. To provide anelectrically balanced winding pattern, each of the parallel windingsneeds to be in each central slot BB an equal number of times, in eachcentral slot CC an equal number of times, in each outer slot AA an equalnumber of times and in each outer slot DD an equal number of times. Fora stator having more slots per pole per phase, the same pattern appliesfor the parallel wires to be electrically balanced.

Wires A, B, C are also subject to position change end loops. Morespecifically, and as can be seen in FIGS. 2 and 3, at the point wherewires A, B, C shift from layer 2 to layer 3, the end loops extendingbetween poles 15 and 16 are position change end loops. This positionchange involves wire A having a position change end loop with a pitch of11 slots, wire B having a position change end loop with a pitch of 8slots and wire C having a position change end loop with a pitch of 8slots. Each of these position change end loops also move wires A, B, Cfrom layer 2 at pole 15 to layer 3 at pole 16. Thus, wire A moves fromslot AA at pole 15 to slot CC at pole 16, wire B moves from slot BB atpole 15 to slot AA at pole 16 and wire C moves from slot CC at pole 15to slot BB at pole 16.

Wires A, B, C are subject to a second position change at the intervalbetween poles 7 and 8 in layer 4. This position change involves wire Ahaving a position change end loop with a pitch of 7 slots, wire B havinga position change end loop with a pitch of 10 slots and wire C having aposition change end loop with a pitch of 10 slots. Thus, wire A movesfrom slot DD at pole 7 to slot BB at pole 8, wire B moves from slot BBat pole 7 to slot CC at pole 8 and wire C moves from slot CC at pole 7to slot DD at pole 8.

Wires A, B, C are subject to a third position change at the intervalbetween poles 7 and 8 in layer 6. This position change involves wire Ahaving a position change end loop with a pitch of 11 slots, wire Bhaving a position change end loop with a pitch of 8 slots and wire Chaving a position change end loop with a pitch of 8 slots. Thus, wire Amoves from slot BB at pole 7 to slot DD at pole 8, wire B moves fromslot CC at pole 7 to slot BB at pole 8 and wire C moves from slot DD atpole 7 to slot CC at pole 8.

As mentioned above, the wiring diagrams in FIGS. 1 and 2 label any pitchbetween slot segments that is non-standard. The location of the numberindicating the non-standard pitch also indicates at which axial end ofthe stator the end loop forming the non-standard pitch is located. FIGS.1 and 2 also show from which axial end of the stator the beginning andend of wires A, B, C, X, Y, Z extend. As can be seen in FIG. 1, theposition change end loops for wires X, Y, Z are all at the same axialend of the stator assembly as the start and finish lead ends of wires X,Y, Z with the phase shift end loops being positioned on the oppositeaxial end of the stator assembly. Similarly, as can be seen in FIG. 2,the position change end loops for wires A, B, C are all at the sameaxial end of the stator assembly as the start and finish lead ends ofwires A, B, C with the phase shift end loops being positioned on theopposite axial end of the stator assembly. The start and finish leadends and position change end loops of wires A, B, C, X, Y, Z are all onthe same axial end of the stator assembly while the phase change endloops of wires A, B, C, X, Y, Z are all on the opposite side of thestator assembly.

It is additionally noted that when position change end loops are usedwith the wires, the individual wire having the largest pitch will beextended further axially than the wires with the shorter pitches andwill have an end loop that extends over the shorter pitch and axiallyshorter end loops. In other words, if three wires have position changeend loops with two wires having a pitch of 8 and one having a pitch of11, the wire having a pitch of 11 will be extended axially further fromthe stator core than the two wires with the pitch of 8 and the end loopof the wire having a pitch of 11 will extend over the other two wireshaving a pitch of 8 to thereby avoid spatial conflicts between thewires.

While the described position change end loops are used to electricallybalance the windings, it is noted that the wires A, B, C, X, Y, Z arenot individually electrically balanced but once they are seriallyconnected in pairs, the three resulting parallel windings areelectrically balanced. In other words, each winding is formed by aseries connection between two individual unbalanced wires to form abalanced winding. This is further discussed below with reference toTables 3 and 4.

The wires are connected together at their finish ends. Thus, the end ofwire A extending from layer 6 at pole 15 is connected in series with theend of wire Z extending from layer 6 at pole 16; the end of wire Bextending from layer 6 at pole 15 is connected in series with the end ofwire X extending from layer 6 at pole 16; and the end of wire Cextending from layer 6 at pole 15 is connected in series with the end ofwire Y extending from layer 6 at pole 16. The start leads of each of thewires are connected with an external circuit member. For example, startleads A, B and C may all be attached to a neutral connection with startleads X, Y and Z all being attached to a regulator, inverter or othercircuit member. The start leads of the A, B and C wires all extend fromlayer 1 of pole 16 and are conductively coupled together, similarly, thestart leads of the X, Y and Z wires all extend from layer 1 of pole 1and are conductively coupled together. As a result the first winding(formed by the series connected pair of wires A and Z), the secondwinding (formed by the series connected pair of wires B and X), and thethird winding (formed by the series connected pair of wires C and Y) arearranged in parallel. It is further noted that in the illustratedembodiment, each of the series connections, i.e., between A and Z,between B and X and between C and Y, is also a reversing connection withone of the wires extending in a clockwise direction about the statorfrom the series connection and the other wire extending in acounterclockwise direction about the stator from the series connection.

As can be understood with reference to the tables presented below, thewinding pattern described above and shown in figures provides anelectrically balanced stator assembly.

Table 1 presented below provides a detailed summary of the windingpattern for wires A, B, C of the winding pattern for wires X, Y, Z of asingle phase of three phase electric machine 20.

TABLE 1 Winding Pattern for Wires A, B, C Slot Slot Slot Slot Slot TurnLayer Group AA BB CC DD Start 1 1 16 A B C Layer Change 1 2 1 A B C 1 22 A B C 1 2 3 A B C 1 2 4 A B C 1 2 5 A B C 1 2 6 A B C 1 2 7 A B C 1 28 A B C 1 2 9 A B C 1 2 10 A B C 1 2 11 A B C 1 2 12 A B C 1 2 13 A B C1 2 14 A B C 1 2 15 A B C Layer and Position 2 3 16 B C A Change SlotShift and 2 4 1 B C A Layer Change 2 4 2 B C A 2 4 3 B C A 2 4 4 B C A 24 5 B C A 2 4 6 B C A 2 4 7 B C A Position Change 2 4 8 A B C , 2 4 9 AB C 2 4 10 A B C 2 4 11 A B C 2 4 12 A B C 2 4 13 A B C 2 4 14 A B C 2 415 A B C Layer Change 3 5 16 A B C Layer Change 3 6 1 A B C 3 6 2 A B C3 6 3 A B C 3 6 4 A B C 3 6 5 A B C 3 6 6 A B C 3 6 7 A B C PositionChange 3 6 8 B C A 3 6 9 B C A 3 6 10 B C A 3 6 11 B C A 3 6 12 B C A 36 13 B C A 3 6 14 B C A Finish 3 6 15 B C A

Table 2 presented below provides a detailed summary of the windingpattern for wires X, Y, Z of a single phase of three phase electricmachine 20.

TABLE 2 Winding Pattern for Wires X, Y, Z. Slot Slot Slot Slot Slot TurnLayer Group AA BB CC DD Start 1 1 1 X Y Z 1 1 2 X Y Z 1 1 3 X Y Z 1 1 4X Y Z 1 1 5 X Y Z 1 1 6 X Y Z 1 1 7 X Y Z 1 1 8 X Y Z Position Change 11 9 Y Z X 1 1 10 Y Z X 1 1 11 Y Z X 1 1 12 Y Z X 1 1 13 Y Z X 1 1 14 Y ZX 1 1 15 Y Z X Layer Change 1 2 16 Y Z X Layer Change 2 3 1 Y Z X 2 3 2Y Z X 2 3 3 Y Z X 2 3 4 Y Z X 2 3 5 Y Z X 2 3 6 Y Z X 2 3 7 Y Z X 2 3 8Y Z X Position Change 2 3 9 X Y Z 2 3 10 X Y Z 2 3 11 X Y Z 2 3 12 X Y Z2 3 13 X Y Z 2 3 14 X Y Z 2 3 15 X Y Z Slot Shift and 2 4 16 X Y Z LayerChange Layer Change and 3 5 1 Y Z X Position Change 3 5 2 Y Z X 3 5 3 YZ X 3 5 4 Y Z X 3 5 5 Y Z X 3 5 6 Y Z X 3 5 7 Y Z X 3 5 8 Y Z X 3 5 9 YZ X 3 5 10 Y Z X 3 5 11 Y Z X 3 5 12 Y Z X 3 5 13 Y Z X 3 5 14 Y Z X 3 515 Y Z X Layer Change and 3 6 16 Y Z X Finish

Table 3 provides a summary of the slot locations for each of wires A, B,C, X, Y, Z of a single phase of three phase electric machine 20 andillustrates how each of these individual wire are unbalanced.

TABLE 3 Slot Totals by Wire Slot AA Slot BB Slot CC Slot DD Total for A16 16 1 15 Total for B 1 31 16 0 Total for C 0 1 31 16 Total for X 15 116 16 Total for Y 16 31 1 0 Total for Z 0 16 31 1

Table 4 provides a summary of the slot locations for each of theparallel windings which are formed by a series connection between a pairof the individual wires for a single phase of three phase electricmachine 20. More specifically by joining wires A and Z into a singleelongate filar, by joining wires B and X into a single elongate filarand by joining wires C and Y into a single elongate filar. Table 4 alsodemonstrates that the three resulting windings are electricallybalanced.

TABLE 4 Slot Totals by Winding Slot AA Slot BB Slot CC Slot DD A and Z16 + 0  16 + 16  1 + 31 15 + 1 B and X 1 + 15 31 + 1  16 + 16  0 + 16 Cand Y 0 + 16  1 + 31 31 + 1  16 + 0As can be seen from Table 4, the central to outer slot ratio for thewindings is 2:1 but, as can be understood with reference to Table 3, theratio between central slot and outer slot for the individual wires A, B,C, X, Y, Z are not 2:1. Table 4 shows how each individual unbalancedwire can be connected in series with another individual unbalanced wireto form a balanced winding.

FIGS. 7A through 9C illustrate end loops that can be used to achieve thewinding pattern described above. It is first noted that FIGS. 7A-9C showthe end loops of three wires as those end loops extend from a selectedpole (pole A) to the next adjacent pole (pole B).

FIGS. 7A-7C illustrate the situation where three wires each define astandard pitch between the two poles. This is the most commonarrangement of the end loops for the depicted electric machine. In thissituation with all of the wires having a standard pitch, the wiresmaintain their same relative position in the two poles A, B. FIG. 7B, 7Cillustrate this by showing fourth slot 50 of poles A and B. It is notedthat while this empty slot 50 is shown on the left of the wires in FIGS.7B, 7C, it will be on the right side of the wires at other locations.

When the wires undergo a phase shift and all of the wires have phaseshift end loops, the pitch of each of the wires will differ from thestandard pitch by one slot and the arrangement of the wires will lookthe same as depicted in FIGS. 7A-7C with each wire of the three wiresdefining the same pitch. For example, if the wires had an empty slot 50at the left end at pole A and it was desired to shift the wires so thatthere was an empty slot 50 on the right end of pole B without changingthe relative positions of the three wires, the wires would all be givena pitch of 8 (one less than the standard pitch). Alternatively, thewires could all be given a pitch of 10 (one more than the standardpitch) to move them from the three left slots of pole A to the threeright slots of pole B without changing their relative positions.

FIGS. 8A-8C and FIGS. 9A-9C illustrate situations wherein each of thewires have a position change end loop. FIGS. 8A-8C illustrate thesituation where one wire has a pitch less than the standard pitch andtwo wires have a pitch greater than the standard pitch while FIGS. 9A-9Cillustrate the situation where one wire has a pitch greater than thestandard pitch and the other two wires have a pitch less than thestandard pitch. In each of these situations, the wires defining agreater pitch extend over the top of the wires having a less thanstandard pitch.

Turning specifically to FIGS. 8A-8C, the set of position change endloops depicted in these figures a first wire 52 moves from the right endof the wires at pole A to the left end of the wires at pole B. Toaccomplish this, first wire 52 has a pitch of 7, two less than thestandard pitch while the remaining wires 54 each have a pitch of 10, onemore than the standard pitch. This maintains the three wires, as awhole, in the same slots of poles A and B while rearranging theindividual wires within those slots. In other words, the empty slot 50of the pole is at the same side of pole A and pole B. FIGS. 8B and 8Cillustrate the empty slot 50 being at the left end but the depictedarrangement of the wires in FIGS. 8A-8C will also maintain the emptyslot at the right end of the poles.

While the depicted electric machine has three parallel windings perphase, alternative embodiments may include a lesser or larger number ofparallel windings. To move one winding from the leading end of wires (atpole A) to the trailing end of the wires (at pole B) as depicted inFIGS. 8A-8C, the appropriate end winding, e.g., winding 52, is given apitch that is equal to the standard pitch minus the number of remainingwindings 54. In the case of FIGS. 8A-8C this will be 9-2 or 7 while theremaining wires are given a pitch that is equal to the standard pitchplus one or 9+1=10. Another way to state this formula is that winding 52will have a pitch equal to the standard pitch, plus one and minus thetotal number of windings, or, (9+1)−3=7. The remaining windings are allshifted one slot to make room for winding 52 and, as mentioned above,have a pitch that is equal to the standard pitch plus 1. By giving theremaining windings 54 all the same pitch, these remaining wires 54maintain their positions relative to each other.

As can be most easily seen in FIGS. 8B and 8C, the remaining wires 54extend a greater axial distance away from the stator core and over wire52. It also noted that similar to the wires of FIGS. 7A-7C, theremaining wires 54 have staggered apexes and a radially extending centersection proximate the apex that allows them to overlap each other.

It is noted that, for the exemplary embodiment, the 7 and 10 pitch endloops depicted in FIGS. 8A-8C are employed with wires X, Y, Z in themiddle of layer 3 (FIG. 1) and with wires A, B, C in the middle of layer4 (FIG. 2). These sets of end loops are also present in FIG. 5, betweenpoles 7 and 8, layer 4 for wires A, B, C and between poles 8 and 9,layer 3 for wires X, Y. Z.

Turning now to FIGS. 9A-9C, this set of end loops moves a first wire 56from the left end of the wires at pole A to the right end of the wiresat pole B. To accomplish this, first wire 56 has a pitch of 11, two morethan the standard pitch while the remaining wires 58 each have a pitchof 8, one less than the standard pitch. This maintains the three wires,as a whole, in the same slots of poles A and B while rearranging theindividual wires within those slots. In other words, the empty slot 50of the pole is at the same side of pole A and pole B. FIGS. 9B and 9Cillustrate the empty slot 50 being at the left end but the depictedarrangement of the wires in FIGS. 9A-9C will also maintain the emptyslot at the right end of the poles.

To move one winding from the trailing end of wires (at pole A) to theleading end of the wires (at pole B) as depicted in FIGS. 9A-9C, theappropriate end winding, e.g., winding 56, is given a pitch that isequal to the standard pitch plus the number of remaining windings 58. Inthe case of FIGS. 9A-9C this will be 9+2 or 11 while the remaining wiresare given a pitch that is equal to the standard pitch minus one or9−1=8. Another way to state this formula is that winding 56 will have apitch equal to the standard pitch, minus one and plus the total numberof windings, or, (9−1)+3=11. The remaining windings 58 are all shiftedone slot to make room for winding 56 and, as mentioned above, have apitch that is equal to the standard pitch minus 1. By giving theremaining windings 58 all the same pitch, these remaining wires 58maintain their positions relative to each other.

As can be most easily seen in FIGS. 9B and 9C, the first wire 56 extendsa greater axial distance away from the stator core and over the tworemaining wires 58. In both FIGS. 8A-8C and FIGS. 9A-9C it is the wiresthat have a larger pitch that extend over the top of the wires that havea shorter pitch. This arrangement is one that minimizes the spatialconflicts between the wires involved in the position change end loops.It also noted that similar to the wires of FIGS. 7A-7C and the remainingwires 54 of FIGS. 8A-8C, remaining wires 58 have staggered apexes and aradially extending center section proximate the apex that allows them tooverlap each other.

It is noted that, for the exemplary embodiment, the 8 and 11 pitch endloops depicted in FIGS. 9A-9C are employed with wires X, Y, Z in themiddle of layer 1 (FIG. 1) and with wires A, B, C in the middle of layer6 (FIG. 2). An additional set of end loops that have 8 and 11 pitchesbut which also transition between layers are found at the transitionbetween layers 4 and 5 for wires X, Y, Z (FIG. 1) and at the transitionbetween layers 2 and 3 for wires A, B, C (FIG. 2).

It is noted that while the end loops depicted in FIGS. 9A-9C are usedtwice with each wire (four times with each winding) and the end loopsdepicted in FIGS. 8A-8C are used once with each wire (twice with eachwinding), other combinations of such end loops could also be employed toobtain electrically balanced windings.

Turning now to FIGS. 10A and 10B, these two figures illustrate anarrangement similar to that of FIGS. 9A-9C, but in FIGS. 10A, 10B, twoof the wires 62 have a standard pitch of 9 and remain the same relativeslot positions in both poles. The other wire 60 defines a pitch of 12and moves from a position on the left end of pole A to a position on theright end of pole B. Thus, this arrangement not only alters the relativeposition of the three wires but also shifts all three wires within thepoles from the three trailing slot positions (at pole A) to the threeleading slot positions (at pole B) (a phase shift end loop). This isaccomplished by having wires 62 retain the same slots in pole A and poleB by using a standard pitch with these two wires 62 and having wire 60leapfrog over wires 62 by providing it with a pitch that is equal to thestandard pitch, plus the number of wires over which it must leapfrog (2)plus one to move it into an empty slot, in other words, 9+2+1=12.

Similarly, the wires could be shifted from the leading slot positions tothe trailing slot positions by providing the leading wire at pole A witha pitch of 6 (9−2−1=6) and the other two wires with a pitch of 9. In allof these situations, it will be most convenient to have the wires withthe larger pitch extend over the top of the wires with the smallerpitch.

The depicted wires 62 have a configuration similar to the wires shown inFIGS. 7A-7C and have staggered apexes and a radially extending centersection proximate the apex that allows them to overlap each other.

It is noted that the windings depicted in FIGS. 10A and 10B are notemployed in the exemplary embodiment of FIGS. 1-6, however, the depictedelectric machine could be modified to include windings similar to thatshown in FIGS. 10A and 10B if desired. The use of the end loops shown inFIGS. 10A, 10B provide both a phase shifting and positioning changingfunction and thus the use of a single set of end loops as depicted inFIGS. 10A, 10B could be used to replace both a set of position changeend loops and a set of phase shift end loops with a single set of endloops that combine both of these functions.

It is additionally noted, that while the depicted electric machineincludes end loops that all have a cascaded arrangement, it would alsobe possible to employ interlaced/interleaved end loops (eithercontinuous or hairpin) between poles which require only standard pitchesfor each of the wires and employ end loops as depicted in FIGS. 8A-8C,9A-9C and/or 10A, 10B where appropriate.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles.

What is claimed is:
 1. A multi-phase electric machine comprising: astator operably coupled with a rotor wherein the rotor is rotatablerelative to the stator; the stator including a stator core defining acentral opening and a plurality of axially extending slots whichcircumscribe the central opening; a plurality of windings mounted on thestator core wherein the plurality of windings define a plurality ofphases and wherein, for each phase, the plurality of windings include:at least two parallel windings; the stator assembly defining a standardpitch between each pole of each phase, the pitch being a commoncircumferential spacing between corresponding slots of each pole; andwherein each of the parallel windings includes at least one positionchange end loop, wherein each of the parallel windings has one of theposition change end loops at the same location, wherein the positionchange end loops define a non-standard pitch to thereby change therelative positions of the parallel windings in the slots.
 2. Theelectric machine of claim of claim 1 wherein each phase includes atleast three windings connected in parallel.
 3. The electric machine ofclaim 2 wherein a first set of position change end loops is disposedbetween a selected pole and an adjacent pole and wherein a first windingof the first set of position change end loops is disposed at one of theclockwise and counterclockwise ends of the pole at the selected pole andis disposed at the other of the clockwise and counterclockwise ends ofthe pole at the adjacent pole, the remaining windings of the first setof position change end loops each being shifted one by one slot.
 4. Theelectric machine of claim 3 wherein the first winding defines a pitchthat is greater than the standard pitch between the selected andadjacent poles and the remaining windings each define a pitch that isone less than the standard pitch between the selected and adjacentpoles.
 5. The electric machine of claim 4 wherein the first windingextends over the remaining windings between the selected and adjacentpoles.
 6. The electric machine of claim 5 wherein there are exactlythree windings per phase and the first winding defines a pitch that istwo slots greater than the standard pitch between the selected andadjacent poles.
 7. The electric machine of claim 3 wherein the firstwinding defines a pitch that is less than the standard pitch between theselected and adjacent poles and the remaining windings each define apitch that is one greater than the standard pitch between the selectedand adjacent poles.
 8. The electric machine of claim 7 wherein theremaining windings extend over the top of the first winding between theselected and adjacent poles.
 9. The electric machine of claim 8 whereinthere are exactly three windings per phase and the first winding definesa pitch that is two slots less than the standard pitch between theselected and adjacent poles.
 10. The electric machine of claim 1wherein, at each set of position change end loops, the windings defininga greater pitch extend over the windings defining a lesser pitch. 11.The electric machine of claim 10 wherein the windings define a phaseshift wherein for each pole, there are a greater number of slots thanwindings.
 12. The electric machine of claim 10 wherein each windingincludes a plurality of position change end loops.
 13. The electricmachine of claim 1 wherein the electric machine is a three phaseelectric machine.